Work piece condition detection using flame electrical characteristics in oxy-fuel thermal processing equipment

ABSTRACT

An automated oxy-fuel thermal processing system including an oxy-fuel torch, an automated machine tool operatively coupled to the torch for moving the torch relative to a work piece, and a circuit including a voltage source or a current electrically connected to the torch and configured to be electrically connected to the work piece. The automated oxy-fuel thermal processing system may further include a processor that is operatively connected to the torch, the automated machine tool, the circuit, and the voltage source or current source, wherein the processor is configured to control the operation of the torch, the automated machine tool and the voltage source or current source, and to monitor a current or voltage in the circuit in a predefined manner.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 14/777,313 filed Sep. 15, 2015, now U.S. Pat. No. 10,067,496,which is a national stage application of International PatentApplication No. PCT/US2014/025938 filed Mar. 13, 2014, which claimspriority to U.S. provisional patent application Ser. No. 61/786,956,filed Mar. 15, 2013, titled “Work piece Condition Detection using FlameElectrical Characteristics in Gas Cutting Torches,” the entirety of allof which is incorporated herein by reference.

FIELD OF THE DISCLOSURE

Embodiments of the present invention relate generally to the field ofoxy fuel thermal processing equipment, and more particularly to systemthat can obtain parameters associated with a thermal cutting or weldingprocess using electrical characteristics of the torch flame an oxy fuelthermal processing equipment.

BACKGROUND OF THE DISCLOSURE

Modern automated gas cutting torches are commonly equipped with featuressuch as automatic ignition, automatic standoff control, kindlingtemperature detection, ignition and blowout detection, and neutral flamedetection. Each of these features can be implemented using actuation andsensing mechanisms that should be reliable, economical, and resistant tothe harsh operating environments created when cutting is performed (e.g.high heat, abrasive debris, particulate deposition etc.).

Kindling temperature detection has been successfully achieved usingoptical infrared (IR) sensors directed toward a work piece. Whileoptical sensors are generally effective for such an application, theyare extremely sensitive to abrasion and particulate deposition, and aretherefore commonly mounted within a torch and directed down the torch'scutting oxygen orifice. One problem with this approach is that it cannotbe implemented in cases where the diameter of a torch's cutting oxygenbore is too small to accommodate an optical sensor.

Automatic ignition in gas cutting torches has been achieved bytemporarily re-routing a torch's fuel-oxygen mixture through the torch'scutting bore for a period of time sufficient to allow a flame, ignitedinternally, to propagate to the tip of the torch, where it is allowed tostabilize. This solution requires solenoids to be operatively mountedwithin the torch for adjustably routing the fuel-oxygen mixture.

Various techniques for automatic standoff control are known, each ofwhich is associated with particular shortcomings. For example,capacitive standoff control techniques, such as those described in U.S.Pat. No. 6,251,336, rely on the assumption that a work piece (e.g. asteel plate) is a quasi-infinite surface. Such techniques thereforeperform inconsistently when a cutting torch nears the edges of a workpiece. Inductive standoff control techniques rely on perturbations in aninduced, oscillating magnetic field around a work piece, and aretherefore susceptible to undesirable cross-interference when two torchesare operated near one another. Optical standoff control methods requiresensors that must be mounted on the exterior of a torch, and aretherefore susceptible to being obscured, scratched or otherwise damagedby debris during cutting. Mechanical standoff control methods that usewhiskers or rider plates require large radii in which to operate. Suchmethods may therefore yield inconsistent results when performed adjacenta work piece's edges or near areas where two cuts meet.

It is apparent that current approaches for implementing certainadvantageous features of modern gas cutting torches suffer from variousinconsistencies of operation. Moreover, such approaches requireadditional electronics and hardware to be mounted on or inside of a gascutting torch, which can substantially increase the cost of an automatedtorch system while diminishing the reliability of a system. It wouldtherefore be advantageous to provide an automated gas cutting torchsystem that provides features such as kindling temperature detection,automatic ignition, and automatic standoff control, wherein such systemis reliable, economical, and robust.

SUMMARY OF THE DISCLOSURE

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended asan aid in determining the scope of the claimed subject matter.

Various embodiments of the present disclosure are generally directed toan automated oxy-fuel thermal processing system and a method ofoperating the same. In some embodiments the system is an oxy-fuelcutting system. In other embodiments the system is an oxy-fuel weldingsystem.

An oxy-fuel thermal processing system is disclosed. The system includesa driver coupled between first and second surfaces for driving a currentbetween the first and second surfaces, the first and second surfacesexposed to a flame of a torch associated with the oxy-fuel processingsystem. A voltage sensor may be coupled between the first and secondsurfaces for sensing a voltage response to the driven current. Amicroprocessor is in communication with the current driver and thevoltage sensor for receiving driven current and sensed voltage responseinformation, the microprocessor configured to calculate a firstparameter associated with a thermal process based on said receivedcurrent and voltage response information, to determine if the firstparameter is within a predetermined range, and when the first parameteris outside the predetermined range to instruct adjustment of a secondparameter associated with the thermal process.

An oxy-fuel thermal processing system is disclosed. The system includesa voltage source coupled between first and second surfaces for applyinga voltage between the first and second surfaces, the first and secondsurfaces exposed to a flame of a torch associated with the oxy-fuelthermal processing system. A current sensor may be coupled between thefirst and second surfaces for sensing a current response to the appliedvoltage. A microprocessor is in communication with the voltage sourceand the current sensor for receiving applied voltage and sensed currentresponse information. The microprocessor may be configured to calculatea first parameter associated with a thermal process based on saidapplied voltage and sensed current response information, to determine ifthe first parameter is within a predetermined range, and when the firstparameter is outside the predetermined range to instruct adjustment of asecond parameter associated with the thermal process.

A method is disclosed for controlling an oxy-fuel thermal processingprocess, comprising: applying a voltage between first and secondsurfaces while the first and second surfaces are exposed to a flame of atorch; sensing a current generated in response to the applied voltage;and determining a first parameter associated with a thermal processingprocess based on the applied voltage and the sensed current; determiningwhether the first parameter is within a predetermined range, and whenthe first parameter is outside the predetermined range adjusting asecond parameter associated with the thermal processing process.

A method is disclosed for controlling an oxy-fuel thermal processingprocess, comprising: driving a current between first and second surfaceswhile the first and second surfaces are exposed to a flame of a torch;sensing a voltage between the first and second surfaces in response tothe driven current; and determining a first parameter associated with athermal process based on said driven current and sensed voltage;determining whether the first parameter is within a predetermined range,and when the first parameter is outside the predetermined rangeadjusting a second parameter associated with the thermal process.

In some embodiments the disclosed system may include a cutting torch, anautomated machine tool operatively coupled to the cutting torch formoving the cutting torch relative to a work piece, and a sensing circuitincluding a voltage source electrically connected to the torch andconfigured to be electrically connected to the work piece. The sensingcircuit further includes a processor that is in communication with thecutting torch, the automated machine tool, the circuit, and the voltagesource. The processor may be configured to control the operation of thecutting torch, the automated machine tool, and the voltage source and tomonitor a current in the circuit in a predefined manner.

A method for operating a cutting torch system is also disclosed. In someembodiments the method may include outputting a voltage from a voltagesource that is electrically connected in series with a cutting torch anda work piece being cut by the cutting torch, lowering the cutting torchtoward the work piece until current flows between a tip of the gascutting torch and the work piece, indicating that a tip of the cuttingtorch has reached a zero height at which the tip is in contact with thework piece.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example, specific embodiments of the disclosed device will nowbe described, with reference to the accompanying drawings, in which:

FIG. 1 is a cross-section view of an exemplary oxy-fuel cutting tip;

FIG. 2 is a schematic view of an exemplary cutting flame and twosurfaces with voltage source and shunt;

FIG. 3 is a hypothetical current-voltage (I-V) diagram representative ofoperational behavior of the schematic elements of FIG. 2;

FIG. 4A is a voltage driven sensing system according to an embodiment ofthe disclosure;

FIG. 4B is a current driven sensing system according to an embodiment ofthe disclosure;

FIG. 5 is a schematic illustrating an exemplary technique for locatingthe surface of a work piece using the disclosed system;

FIG. 6 is a schematic illustrating an exemplary technique for measuringan optimum gas mixture for a cutting torch;

FIGS. 7A and 7B are flow diagrams illustrating exemplary methods inaccordance with the disclosure;

FIG. 8 is a schematic view of an exemplary automated cutting system inaccordance with the present disclosure;

FIG. 9 is flow diagram illustrating an exemplary method for operatingthe automated gas cutting system of the present disclosure;

FIG. 10 is a schematic view illustrating an exemplary capacitive energystorage device of the present disclosure;

FIG. 11 is a schematic view illustrating an exemplary inductive energystorage device of the present disclosure; and

FIG. 12 is a schematic view illustrating an exemplary oscillatingvoltage source of the present disclosure.

DETAILED DESCRIPTION

The present disclosure will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This disclosure, however, may be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the disclosure to those skilled in the art. In thedrawings, like numbers refer to like elements throughout.

The oxy-fuel cutting process is used to cut material that reacts withoxygen by heating the material to a kindling temperature, and thenburning the material away in an oxygen-rich atmosphere. To achieve this,as shown in FIG. 1 an oxy-fuel cutting torch 1 can comprise a longcylinder 2 with internal passages 4, 6 configured to deliver gaseousfuel (e.g., acetylene, propane, or the like) and oxygen, respectively,to a nozzle 8, mounted at the cylinder's bottom. The nozzle 8 can issuea premixed combustible mixture from an array of ports 10 arranged arounda central port 12 from which pure oxygen is issued.

To begin a cut, the torch 1 is positioned a distance above a work piece14. The torch 1 may be operating with a stable flame 16 (FIG. 2)oriented downward at the work piece 14. At this point oxygen is notsupplied through the central port 12. Rather, the flame 16 may be usedto heat the work piece 14 until it is hot enough that the material willburn in an oxygen atmosphere. The critical temperature needed for a cutto successfully begin is referred to as the “kindling temperature.” Whenthe work piece 14 reaches its kindling temperature, oxygen is suppliedvia the central port 12. If the work piece 14 is sufficiently hot, itwill ignite and the flow of oxygen will pierce the work piece. If thework piece 14 is too cool, however, the flow of oxygen will only serveto further cool the material and the heating process will have to berepeated before cutting can be performed. As will be appreciated, inorder to obtain an efficient process, it is important to accuratelydetermine when the work piece is ready for cutting (i.e., when thematerial of the work piece has reached its kindling temperature).

Once piercing of the work piece 14 is accomplished, the torch 1 can thenbe moved along a desired cut path to cut the work piece into a desiredshape. Generally speaking, as the flame 16 advances through the workpiece, the material in front of the flame is relatively cool, and thusit must be brought up to the kindling temperature in order to enable itto be cut by the flame. The process relies on the preheat flame, butparticularly relies on the heat released from the cut itself. As will beappreciated, if the torch 1 is advanced too quickly the heat releasedfrom the cut may not have sufficient time to conduct into thesurrounding plate, and the temperature of the surface inside theadvancing cut will fall. If the temperature drops too low thencombustion may stop, and the preheat process will need to be repeated torestart the cut.

There are a number of practical issues that arise when attempting toautomate an oxy-fuel cutting process. Before the process is begun, thetorch 1 is ignited and the flow of fuel and oxygen brought into desiredproportions. The torch 1 is then brought to a predetermined height abovethe work piece and allowed to bring the material to its kindlingtemperature. The specific height and the timing of the process can beimportant to the successful initiation of a cut.

To accomplish these functions, cutting systems often include automatedand/or manual adjustment mechanisms for moving the torch 1 in twohorizontal axes (x-y) in order to generate a cut path on a work piecesuch as a flat plate. The adjustment mechanism may also be configuredfor adjusting the height of the torch 1 relative to the work piece. Suchadjustment mechanisms are known in the art, and thus will not bedescribed in detail herein. It will be appreciated that the disclosedsystem not limited to use with such mechanisms, there are many potentialembodiments that include them.

As described, the oxy-fuel cutting process can include a series ofoperations including a number of steps that rely on feedback, eitherfrom a human operator or from an appropriately robust suite of sensorsand controls. For example, feedback can be desirable to facilitateadjusting the torch's fuel-oxygen mixture to achieve a desired “neutralflame.” During the preheat operation, if sensor feedback indicates thework piece 14 temperature is not determinable (e.g., due to sensorerror), the operator must visually observe the glow of the work piece,or an automated system must be programmed to wait for an additionalperiod of time to ensure that the work piece has achieved its kindlingtemperature so that cutting will successfully start. In another example,a standoff distance “SD” between the torch 1 and the work piece 14depends on feedback control since the standoff can be on the order of aninch or less, and the torch may be positioned many feet from theoperator making visual observation difficult or inconvenient.

While a desired level of feedback can be obtained by mounting sensors onor around the torch, the volatile environment of the oxy-fuel cuttingsystem necessitates sensors that are hardened against electrical noise,thermal stresses, abrasion and impact. As a result such sensors areoften either very vulnerable to damage and/or are very expensive.

In the context of a torch flame 16, an electrical potential appliedbetween two surfaces that are otherwise electrically isolated (e.g., thetorch 1 and the work piece 14) will result in a flow of current throughthe torch flame. This relationship can be measured using an arrangementsuch as that shown in FIG. 2, illustrating the torch 1, the torch flame16, a voltage source 18 and a shunt resistor 20. It will be appreciatedthat the voltage source 18 and shunt resistor 20 are but one possibleembodiment, and that other arrangements can also be used. In addition,although the description will proceed in relation to the use of twosurfaces under test (e.g., the torch 1 and the work piece 14), othersensing surface configurations can also be used, and thus the disclosureis not so limited.

The relationship between voltage and current can be divided into threeregimes, shown in FIG. 3. In the central, “linear regime” (II), currentthrough the torch flame is limited by the electrical resistance of thetorch flame which separates the two surfaces 1, 14. As such, the slopeof the characteristic curve in this linear regime (II) is constant.However, as the magnitude of current through the torch flame 16approaches either extreme, it eventually enters a “saturation regime”(I, III). In the saturation regime (I, III), current through the torchflame 16 is limited by the cathode (i.e., negative) surface's capacityto emit electrons.

In the linear regime, the characteristic relationship between currentand voltage (I-V) can, but need not, pass through the origin. Forembodiments in which the two surfaces 1, 14 are made from differentmaterials, or are at different temperatures, they will have a differentaffinity for electrons. As a result, if the circuit represented by FIG.3 is opened, charge will accumulate until the surfaces 1, 14 reach asteady-state “floating potential.” This “floating potential” is thepotential between two surfaces 1, 14 that is necessary to achieve zerocurrent.

The slope in the linear regime (II) is influenced by a number ofcharacteristics including the flame temperature, the gas composition,and especially the distance between the surfaces. The slope of the I-Vcurve is an implicit measurement of the torch flame's electricalresistance in the path between the two surfaces 1, 14. As the surfaces1, 14 approach each other (e.g., as the torch nozzle 8 is moved towardthe work piece 14), or as the concentration of free radicals increasesin the torch flame 16, the resistance of the torch flame dropsdetectably.

The floating potential, on the other hand, is influenced by the surfacematerials and temperature. Thus, for a given pair of surfaces 1, 14 ifthe temperature of one surface is known, then the floating potential canbe assumed to be an indicator of the temperature of the other surface.

The disclosed system and method exploits the electrical conductivity ofthe torch flame 16 to detect parameters important to the cutting process(e.g., torch offset, work piece temperature), while minimizing and/oreliminating the need for physical sensors and/or probes. By imposing an“electrical action,” measuring a resulting “electrical response,” andinterpreting the results, it is possible to extract a great deal ofinformation on the oxy-fuel process.

In some embodiments the electrical action can take the form of either anapplied voltage or a driven current, with the resultant measurementbeing a measured current or measured voltage, respectively. FIG. 4Ashows one exemplary non-limiting embodiment of a system 22 in which avoltage source 24 applies the electrical action, a current sensor 26such as a shunt measures the current response, and a processor 28collects a series of measurements and computes various parameters. Anon-limiting exemplary list of directly measured parameters includeslinear slope, floating potential, upper/lower saturation current,upper/lower saturation voltage and upper/lower saturation slope. Anon-limiting exemplary list of derived parameters includes standoffdistance “SD,” standoff error, flame mixture quality, cut speed error,imminent cut loss, successful ignition, and work piece temperature.These parameters may be communicated to one or more dependent systems29. A non-limiting exemplary listing of such dependent systems 29includes a torch height controller, motors for positioning the torchvertically with respect to the work piece, motors for moving the torchin the x-y axis with respect to the work piece, a cut speed controller,a gas flow controller, valves regulating the flow of gases, an operatordisplay and a master CNC responsible for control of any or all of theaforementioned systems. FIG. 4B illustrates an alternate embodiment ofthe disclosed system 30 in which current is driven in lieu of voltage.In this embodiment a current source 32 applies the electrical action, avoltage sensor 34 measures the voltage response, and a processor 36collects a series of measurements and computes various parameters, whichhave been previously identified. In both examples, the imposition of anelectrical action and measurement of an electrical response is used tointerrogate the system's I-V characteristic, as will be described below,to obtain information about the operation of the system.

There are two fundamental measurements that are used to derive most ofthe measurements offered by the present disclosure: (1) floatingpotential, and (2) linear slope. Others are also possible, such assaturation threshold current, saturation threshold voltage, and theslope in the saturation regions, but the inventor has found that thelinear regime characteristics appear to be the most reliable.

One non-limiting exemplary method for measuring the floating potentialis to force the current flow between the surfaces 1, 14 to zero. Oncethe voltage between the two surfaces 1, 14 stabilizes, it is taken asthe floating potential. When driving voltage in lieu of current, themean voltage signal can be adjusted until the mean current is zero. Themean voltage at zero mean current is then taken as the floatingpotential.

One non-limiting exemplary method for measuring slope is by calculation,using two points in the linear regime. For accuracy, it may be desirablethat the two points be as different in value as possible while remainingin the system's linear regime. Operation in the linear regime can bereasonably ensured if the two measurements are made near the floatingpotential.

One non-limiting exemplary method for measuring floating potential andslope simultaneously is to apply an oscillating signal of some definiteamplitude, such that the average current is zero. The average voltagewill be the floating potential, and the ratio of the signal amplitudeswill be the slope.

As previously noted, the standoff height separating the torch 1 from thework piece 14 can be an important parameter in controlling an oxy-fuelcutting process. Prior to the preheat process, the exact location of thework piece surface may not necessarily known. One non-limiting exemplaryembodiment that enables the location of the work piece surface to bedetermined, and a specific height to be maintained, is shown in FIG. 5.The torch 1 and the work piece 14 may constitute the two surfaces undertest, (i.e., as shown in FIGS. 4A and 4B), eliminating the need foradditional probes or sensors. It will be appreciated that any of avariety of surfaces of the torch 1 may be used as one of the surfacesunder test, including the torch nozzle. A dedicated probe mountingsurface (not shown) could also be mounted near the nozzle. In addition,a surface other than the work piece 14 could constitute the othersurface under test. For example, any electrically conductive componentpositioned near the flame 16 could be used. In the illustratedembodiment, the torch 1 can be moved toward the work piece 14 in smallpredetermined increments. At each increment, a slope measurement can berecorded using the system 22, 30 of FIG. 4A or 4B. In one embodimentthese compiled slope values are stored in memory (not shown) associatedwith the processor 28, 36. For example, the compiled slope values may bestored in a look up table in the memory.

In the aggregate, and as shown in FIG. 5, these measurements can form atrend tending to zero resistance for some position of the torch 1 withrespect to the work piece 14. That extrapolated location may representthe position of the torch 1 where the tip of the nozzle 8 is touchingthe work piece 14. During operation of the system (e.g., preheating orcutting), when a particular flame resistance measurement is encountered,that value can be used to determine the position of the work piece 14,or more particularly it can be correlated to a specific standoffdistance “SD” (FIG. 1) between the torch 1 and the work piece 14. Thiscan be performed using a lookup table, or a predetermined standard valuecould be used. The system may make this determination continuously orperiodically during cutting operations to confirm a desired standoffdistance “SD” is maintained. In other embodiments, a pre-existingcompilation of expected values for reference slope may be stored forgiven conditions.

Adjustments in standoff distance “SD” can be made during a cut tocompensate for curvature in the work piece 14 and/or to compensate fordifferences in level between the work piece surface and the cuttingmachine path. When cutting is initiated, the standoff distance “SD”between the torch 1 and the work piece 14 can be “trusted.” As such, aslope determination (using one of the previously described techniques)at the beginning of a cut can establish a reference value. After that,as the cut progresses, subsequent periodic slope determinations (again,using one of the previously described techniques) can be compared withthe reference value and used to generate an error signal and/or an alarmcondition if the determined slope departs from the reference value by apredetermined amount. In this way, the slope determination can act as acontinuous measurement of errors in height.

The disclosed system and method can also be used to assess the gasmixture of the associated torch 1. As the gas mixture is adjusted, avariety of techniques may be used to assess its appropriateness forcutting. In some embodiments the flow of oxygen and fuel can be activelyadjusted to maximize the heat flux into the work piece 14.

In one exemplary embodiment, the torch 1 can brought into position abovethe work piece 14, and the gas mixture can be adjusted while performingslope determinations in the manner previously described. With thismethod, the torch 1 and the work piece 14 are the surfaces under test(i.e., as shown in FIGS. 4A and 4B). The mixture at which the slope isextreme (i.e., a minimum or maximum value) can be used as the point atwhich the flame temperature is highest (since the most desirablecondition may be the condition in which heat flux into the work piece 14is at a maximum).

In an alternative embodiment, illustrated in FIG. 6, two identicalprobes 38, 40 may be placed symmetrically in the torch flame 16 at aheight in the flame similar to where a work piece would be positionedduring operation. In one embodiment, the probes 38, 40 may be a pair oftungsten rods extending into the torch flame 16 from either side.Alternatively the probes 38, 40 could be a pair of air or water cooledcopper or stainless steel tube members. In one non-limiting exemplaryembodiment the probes may be built into the torch 1. Due to thesymmetrical nature of the test, the floating potential between theprobes 38, 40 is very small, making the measurement simpler. The gasmixture at which the slope is extreme can be used as an approximationfor the point at which the flame temperature is highest. In thisembodiment, it is desirable that the measurement be performed at alocation in the torch flame 16 that is representative of where the workpiece 14 will ultimately be positioned. It will be appreciated thatchanges in gas mixtures and flow rates can make the flame grow andshrink drastically. As such, changes that actually cool the flame canregister more extreme slopes if the hottest part of the flame has movedto the proximity of the probes.

Measured and/or calculated values of slope measurement and fuel-oxygenmixture can be used by the processor 28, 36 to determine an optimumfuel-oxygen mixture setting, as shown in the graph of FIG. 6.

The disclosed system and method can, in some embodiments, be used tomeasure the temperature of a work piece 14. Thus, the torch nozzle 8 andthe work piece 14 may be used as the measurement surfaces (i.e.,surfaces 1, 14 shown in FIGS. 4A and 4B). During preheating of the workpiece 14, the nozzle 8 on the torch 1 is already at its steady statetemperature. Meanwhile the temperature of the work piece will be rising.Since all other factors that influence the floating potential are heldconstant, the floating potential can be used as an indicator for thework piece temperature during preheat. In fact, as the work piece 14heats up, the floating potential can actually be observed to stabilizefor a brief period as the work piece surface becomes molten. When thefloating potential crosses a certain threshold appropriate to thematerial, the nozzle, and the gas composition, cutting can begin. Insome embodiments the threshold value or values (kindling temperature,floating potential) will be predetermined and stored in memory.

It has been established how the disclosed system and method may be usedto monitor the standoff distance “SD” between the torch 1 and work piece14 during a cutting process. In some embodiments the system and methodcan, in addition or alternatively, be used to diagnose the “health” ofthe cutting process. As the material in the cutting oxygen stream cools,the floating potential will decline. If the floating potential dropsbelow a threshold appropriate to the nozzle, gas composition and flowrate, it can be used as an indicator that the cutting process isproceeding too fast, and should be slowed in order to maintainappropriate cutting parameters. In some embodiments the threshold valueor values (kindling temperature, floating potential) will bepredetermined and stored in memory.

Some embodiments of the disclosed system and method may be used todetect cutting flame ignition. When lighting a torch flame, regardlessof the ignition process, it is not always clear whether a stable flamehas been struck. A spark may have failed to be struck, or the flame mayhave blown off of the tip, or any number of other problems may prevent afirst attempt from yielding a stable flame. As a result, it is desirableto check that ignition was successful. With the disclosed system andmethod, any two conductive surfaces in the vicinity of where a stableflame should be can be monitored. Failure to detect conduction in thepresence of a potential substantially higher than a reasonable floatingpotential (e.g., 10 V) indicates that ignition has failed. In oneembodiment the two conductive surfaces could be the torch 1 and the workpiece 14.

FIG. 7A is a flow diagram illustrating an exemplary method according tothe disclosure. At step 100, a voltage is applied between first andsecond surfaces associated with an oxy-fuel cutting system. In someembodiments the first and second surfaces are a torch surface and a workpiece, respectively. The first and second surfaces may be exposed to theflame of an oxy-fuel torch during operation. At step 110, a currentgenerated in response to the applied voltage is sensed. At step 120, afirst parameter associated with a cutting process is determined based onthe applied voltage and the sensed current. At step 130, a determinationis made about whether the first parameter is within a predeterminedrange. At step 140, if it is determined that the first parameter isoutside the predetermined range, a second parameter associated with thecutting process is adjusted.

FIG. 7B is a flow diagram illustrating an exemplary method according tothe disclosure. At step 150, a current is driven between first andsecond surfaces associated with an oxy-fuel cutting system. In someembodiments the first and second surfaces are a torch surface and a workpiece, respectively. The first and second surfaces may be exposed to theflame of an oxy-fuel torch during operation. At step 160, a voltagegenerated in response to the driven current is sensed. At step 170, afirst parameter associated with a cutting process is determined based onthe driven current and the sensed voltage. At step 180, a determinationis made about whether the first parameter is within a predeterminedrange. At step 190, if it is determined that the first parameter isoutside the predetermined range, a second parameter associated with thecutting process is adjusted.

Referring now to FIG. 8 shows a non-limiting exemplary automatedoxy-fuel cutting torch system 50 (hereinafter “cutting system 50”) inaccordance with the present disclosure. The torch system 50 may includea gas cutting torch 52 (hereinafter “the torch 52”) that is operativelymounted to a computer numerical control (CNC) machine 54 or otherautomated machine tool that is capable of moving the torch 52 along apredefined path, such as may be specified in a software file. The torch52 is shown generically connected to the CNC machine 14, but it will beappreciated that in practical application the torch 52 will be mountedto the CNC machine 54 in a manner that facilitates 2-dimensional or3-dimensional movement of the torch 52 as further described below. Thetorch 52 may be any type of gas cutting torch, including, but notlimited to, an oxy-fuel torch, a propane torch, a propylene torch, abutane torch, or a mixed-fuel torch.

The cutting system 50 may also include a controller 56, which in oneembodiment comprises a microprocessor. The controller 56 may include acircuit 58 including an electrical power source 60 connectedelectrically in series with a resistor 62 or other current or voltagemeasurement device. The power source 60 may be a voltage source or acurrent source. For the sake of convenience, the following descriptionof the cutting system 50 and the accompanying method shall assume thatthe power source 60 is a voltage source, in which case a current may beinduced and measured in the circuit 58 as further described below.However, it will be understood that the power source 60 mayalternatively be a current source, in which case a voltage may beinduced and measured between the torch 52 and a work piece 66 (describedbelow).

During operation of the cutting system 50, one side of the circuit 58may be electrically connected to the torch 52, such as by a firstconductor 64, and the other side of the circuit 58 may be electricallyconnected to a work piece 66 that is to be cut by the torch 52, such asby a second conductor 68. The circuit 58 may further include a switch 70for connecting the torch 52 to ground when the cutting system 50 it isnot in operation, thereby preventing the buildup of static electricityin the circuit 58. The circuit 58 may include additional switches (asshown in FIGS. 10-12) for placing the torch in and out of electricalcommunication with circuits for ignition as further described below.

The controller 56 may further include a processor 72 that is capable ofexecuting a number of predefined instructions. The processor 72 may beoperatively connected to the power source 60 for regulating an amount ofvoltage output therefrom as further described below, and may also beelectrically coupled the circuit 58, such as at points A and B, formeasuring an amount of current flowing in the circuit 58. The processor72 may further be operatively connected to the CNC machine 54 and to thetorch 52 for controlling/modifying the operation thereof as described ingreater detail below. The processor 72 may further be operativelyconnected to the switch 70 for controlling the operation thereof, suchas for selectively moving switch between a closed position, wherein thetorch 52 is connected to the circuit 58 (e.g. when the cutting system 50is in use), and an open position, wherein the torch 52 is connected toground (e.g. when the cutting system 50 is not in use). A non-volatilememory (not shown) may be associated with the processor 72 for storingsoftware instructions executed by the processor 72 and/or for storingdata collected from the circuit 58.

Referring to FIG. 9, a flow diagram illustrating an exemplary method ofoperating the cutting system 50 in accordance with the presentdisclosure is shown. Generally, the method exploits the electricallyconductive nature of the torch's flame to determine the state of thework piece 66 being cut before and during cutting. Particularly, thehigh-temperature gases present in the torch's flame are sufficientlydissociated so that if a voltage is applied between the torch 52 and thework piece 66 a current will flow through the flame. This principle willbe described in greater detail below in the context of the exemplarymethod.

At a first step 200 of the exemplary method, the work piece 66 may bemanually or automatically positioned below the unlit torch 52 andconnected to the circuit 58, such as by the conductor 68. For example,the conductor 68 may be connected to the work piece through the table,such as by an alligator clip or some similar means of electricallyconductive attachment. The nozzle 74 of the torch may initially bedisposed well above the surface of the work piece 66, such as at astandoff distance “SD” of 6-12 inches, for example. If the switch 70 isin the open position, the processor 72 may direct the switch to move tothe closed position, thereby placing the torch in electricalcommunication with the circuit 58.

At step 210 of the method, the processor 72 may command the power source60 to output a relatively low voltage, a non-limiting example of whichis 12V. The processor 72 may then command the CNC machine 54 to slowlylower the unlit torch 52 until the processor 72 detects current flowingin the circuit 58 between connection points “A” and “B”, indicating thatthe nozzle 74 of the torch 52 has been brought into contact with thework piece 66 to complete the circuit 58. The processor 72 may thenrecord the height of the torch 52 in this position as a “zero height”(i.e. the height of the upper surface of the work piece 66). This heightmay be stored in volatile or non-volatile memory associated with theprocessor.

At step 220 of the method, the processor may command the CNC machine 54to elevate the torch 52 away from the work piece 66. The processor 72may simultaneously direct the power source 60 to charge an energystorage device (described below) that is electrically connected withinthe circuit 58. For example, referring to FIG. 10, the energy storagedevice may be a capacitor bank 78, in which case one or more capacitorsin electrical communication with the torch 52 and some other surface(e.g. the work piece 66) may be charged in advance to a predeterminedvoltage and discharged when the CNC machine 54 moves the torch 52 intocontact with said surface.

Alternatively, referring to FIG. 11, the energy storage device may be aninductor 80 that is in electrical communication with the torch 52, inwhich case a switch 82 may be closed to induce a current in an inductor80, wherein the energy stored in the inductor 80 is discharged once thetorch 52 is moved into the proximity of the work piece 66 or othersurface and the switch 82 is opened.

In either case (i.e. either a capacitive or inductive energy storagedevice), if the processor 72 has commanded activation of a flow of gasfrom the torch 52 (e.g. by actuation of appropriate solenoid valves),and has properly positioned the torch 52 in advance, then theabove-described discharge of electrical energy may create an ignitionsite in the gap between the torch 52 and the work piece 66 or othersurface, thereby igniting the stream of gas flowing therethrough. Thisprocess may be enhanced by imposing some combination of oscillatingvoltages or high voltages to increase the gap distances over whichignition can occur, as shown in FIG. 12.

At step 230 of the method, the processor 72 may detect successfulignition of the gas by directing the voltage source to output arelatively low voltage, a non-limiting example of which is 24V, afterdischarge of the capacitors. If the fuel gas was successfully ignited bythe discharge, a small current will flow through the flame 76 and willbe detected by the processor 72 between points “A” and “B” in thecircuit 58. If, by contrast, ignition was not successful, there will beno flame 76 and therefore no detectable current in the circuit 58. Inthe case of ignition failure, the processor 72 may repeat the entireignition process (i.e. step 220 of the method) until successful ignitionis detected.

At step 240 of the method, the processor 72 may direct the CNC machine54 to raise the torch 52 until the nozzle 74 reaches a predefinedstandoff distance “SD” relative to the known zero height (i.e. thesurface of the work piece 66). The processor 72 may then direct thepower source 60 to output a low voltage, a non-limiting example of whichis 12V. At such a low voltage, the current in the circuit 58 will bedetermined by the resistance of the path between the torch 52 and thework piece 66 or some other surface. Such resistance is highly sensitiveto variations in the quality of the flame 76. Thus, the gas mixture inthe torch 52 (e.g. the ratio of fuel gas to oxygen) may be adjusteduntil a desired current value in circuit 58, as determined by theprocessor 72, is achieved at the predefined standoff distance “SD”,where this desired current value is indicative of a desired quality offlame 76. In one non-limiting exemplary embodiment, the desired currentvalue may be indicative of a flame 76 that is suited for preheating thework piece 66 prior to cutting.

At step 250 of the method, the processor 72 may command the CNC machine54 to move the torch 52 to a designated location along the surface ofthe work piece 66 where cutting is to begin. The processor 72 may thenadjust the voltage in the circuit 58 to maintain a constant current,such as may be achieved by directing the CNC machine 54 to adjust thestandoff distance “SD.” That is, when the standoff distance “SD” isincreased, the voltage in the circuit 58 increases and the current inthe circuit 58 decreases. Conversely, when the standoff distance “SD” isdecreased, the voltage in the circuit 58 decreases and the current inthe circuit 58 increases. The processor 72 may in this way utilize themeasured current in the circuit 58 to maintain a consistent standoffdistance “SD” relative to the work piece regardless of variations in thesurface of the work piece 66. This principle is described in U.S. Pat.Nos. 4,328,049 and 3,823,928, the disclosures of which are incorporatedherein by reference.

At step 260 of the method, the processor 72 may command the power source60 to increase its output voltage to a predefined maximum value at whichthe current in the circuit 58 is guaranteed to be limited by electronevaporation from the work piece 66. This predefined maximum value may bedetermined from the geometry and flow rate of the torch 52, for example.Such parameters may be known in advance, and an operator may consult aschedule of voltages or currents that are known to be important. Otherembodiments of the present method may include looking forcurrent-voltage sensitivities (i.e. the relationship between a change incurrent relative to a change in voltage).

With the voltage set at the predefined maximum value, the current in thecircuit 58 will increase coherently with the temperature of the workpiece 66. It will be appreciated by those of skill in the art that whena material, particularly metal, is sufficiently heated, the increasedkinetic energy exhibited by the electrons of the material may allow theelectrons to momentarily escape from the material's boundaries. If ananode that is charged with a sufficiently large voltage is placed in thevicinity of the material, the electrons that escape from the materialwill be pulled away by the charged anode at exactly the same rate atwhich they evaporate from the material. This rate of evaporation isknown to be a function of the temperature of the material.

The current in the circuit 58, as affected by the above-describedelectron evaporation from the work piece 66 and as detected by theprocessor 72, may be used to reliably determine the temperature of thework piece 66. When the measured current reaches a predefined level,such as a level indicative of a kindling temperature in the work piece66, preheating of the work piece 66 is complete and cutting can begin.As will be appreciated by those of ordinary skill in the art, cuttingthe preheated work piece 66 may be achieved by activating the flow ofcutting oxygen.

At step 270 of the method, the CNC machine 54 may move the torch 52along the work piece 66 in accordance with a predefined cutting path atan appropriate speed for maintaining the quality of the cut. As the cutis made, the desired standoff distance “SD” may be maintained bycontinuously performing the torch height adjustment as described in step250 above.

It should be appreciated that certain steps of the above-describedexemplary method may be hindered by inconsistencies and imperfections inthe surfaces of work pieces being cut. For example, oxidation on thesurface of a work piece may form a barrier that resists current flow forcontact sensing (as described in step 210 above) and/or that resistselectrical arcing for torch gas ignition (as described in step 220above). U.S. Pat. No. 7,087,856, which is incorporated herein byreference, describes a method for detecting contact through oxidationlayers on a work piece in a manner that is safe to humans (i.e. thatdoes not involve the application of high voltage or high frequencyenergy for an appreciable amount of time). It is contemplated that sucha method may be similarly implemented in the context of the presentdisclosure for contact sensing and/or for torch gas ignition.

Additionally, the effect of oxidation or surface irregularities may becompensated for by taking initial calibration measurements when the workpiece is in a known condition. A non-limiting example of this would bepositioning the ignited torch 52 above a plate known to be at or nearambient temperature, and applying sufficient voltage so as to drive acurrent limited by thermionic emission from the plate. This calibrationcurrent sensed at this condition is an indication of the platecondition. The kindling temperature can then be recognized by when themeasured current increases by some pre-determined amount relative to thecalibration current.

In view of the forgoing, it will be appreciated that the cutting system50 and accompanying method of the present disclosure provide a number ofimportant advantages relative to existing automated cutting torchsystems. Particularly, the system and method facilitate features such asautomatic standoff control, automatic ignition, ignition detection,flame quality detection, and kindling temperature detection withoutrequiring many of the moving parts, on-board electronics, and sensorsassociated with existing torch systems. The cutting system 50 of thepresent disclosure is therefore far more economical, reliable, androbust than existing systems.

It will be appreciated that although the foregoing description relatedto the specific implementation of the disclosed system and method inrelation to an oxy-fuel cutting apparatus, that the disclosed system andmethod can be implemented in any of a variety of oxy-fuel thermalprocessing apparatus. In one non-limiting example, the disclosed systemand method can be implemented in an oxy-fuel welding apparatus.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralelements or steps, unless such exclusion is explicitly recited.Furthermore, references to “one embodiment” of the present invention arenot intended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features.

Some embodiments of the disclosed device may be implemented, forexample, using a storage medium, a computer-readable medium or anarticle of manufacture which may store an instruction or a set ofinstructions that, if executed by a machine, may cause the machine toperform a method and/or operations in accordance with embodiments of thedisclosure. Such a machine may include, for example, any suitableprocessing platform, computing platform, computing device, processingdevice, computing system, processing system, computer, processor, or thelike, and may be implemented using any suitable combination of hardwareand/or software. The computer-readable medium or article may include,for example, any suitable type of memory unit, memory device, memoryarticle, memory medium, storage device, storage article, storage mediumand/or storage unit, for example, memory (including non-transitorymemory), removable or non-removable media, erasable or non-erasablemedia, writeable or re-writeable media, digital or analog media, harddisk, floppy disk, Compact Disk Read Only Memory (CD-ROM), Compact DiskRecordable (CD-R), Compact Disk Rewriteable (CD-RW), optical disk,magnetic media, magneto-optical media, removable memory cards or disks,various types of Digital Versatile Disk (DVD), a tape, a cassette, orthe like. The instructions may include any suitable type of code, suchas source code, compiled code, interpreted code, executable code, staticcode, dynamic code, encrypted code, and the like, implemented using anysuitable high-level, low-level, object-oriented, visual, compiled and/orinterpreted programming language.

Based on the foregoing information, it will be readily understood bythose persons skilled in the art that the present invention issusceptible of broad utility and application. Many embodiments andadaptations of the present invention other than those specificallydescribed herein, as well as many variations, modifications, andequivalent arrangements, will be apparent from or reasonably suggestedby the present invention and the foregoing descriptions thereof, withoutdeparting from the substance or scope of the present invention.Accordingly, while the present invention has been described herein indetail in relation to its preferred embodiment, it is to be understoodthat this disclosure is only illustrative and exemplary of the presentinvention and is made merely for the purpose of providing a full andenabling disclosure of the invention. The foregoing disclosure is notintended to be construed to limit the present invention or otherwiseexclude any such other embodiments, adaptations, variations,modifications or equivalent arrangements; the present invention beinglimited only by the claims appended hereto and the equivalents thereof.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for the purpose of limitation.

The invention claimed is:
 1. An oxy-fuel thermal processing system, comprising: a torch; a power source; a driver coupled between a first surface of the torch and a second surface of a workpiece, the driver configured to drive the power source to provide a driven power source between the first surface and the second surface, the first surface and the second surface exposed to a flame of the torch during a thermal cutting process; a sensor coupled between the first surface and the second surface, the sensor configured to sense an electric response to the driven power source and provide a sensed electric response; a microprocessor in communication with the driver and the sensor, the microprocessor configured to: receive information about the driven power source and the sensed electric response, calculate a slope of a current-voltage (I-V) relationship associated with a thermal process of the oxy-fuel thermal processing system based on the information about the driven power source and the sensed electric response, determine if the slope is a maximum value in the I-V relationship, and in response to determining that the slope is not the maximum value in the I-V relationship, instruct adjustment of a gas mixture associated with the thermal cutting process; and a switch, controlled by the microprocessor, connecting the torch to ground when the oxy-fuel thermal cutting process is not in operation.
 2. The oxy-fuel thermal processing system of claim 1, wherein the microprocessor is further configured to calculate a first parameter based on the information about the driven power source and the sensed electric response.
 3. The oxy-fuel thermal processing system of claim 2, wherein the first parameter is representative of whether the flame is lit.
 4. The oxy-fuel thermal processing system of claim 3, wherein the first surface is a probe located a predetermined distance from the torch.
 5. The oxy-fuel thermal processing system of claim 4, wherein the probe comprises an ignition system.
 6. The oxy-fuel thermal processing system of claim 2, wherein the power source is a current, the sensor is a voltage sensor, and the microprocessor is configured to calculate the first parameter while thermal processing of the workpiece is being performed.
 7. The oxy-fuel thermal processing system of claim 2, wherein the power source is a voltage, the sensor is a current sensor, and the microprocessor is configured to calculate the first parameter while thermal processing of the workpiece is being performed.
 8. The oxy-fuel thermal processing system of claim 1, further comprising a computer numerical control (CNC) machine connected to the torch, wherein the first surface is movable with respect to the second surface, and wherein the microprocessor is further configured to calculate a distance between the first surface and the second surface based on information about the driven power source and the sensed electric response, to determine if the distance is within a predetermined range, and in response to determining that the distance is outside the predetermined range, to instruct the CNC machine to adjust a height of the torch.
 9. The oxy-fuel thermal processing system of claim 8, wherein the microprocessor is further configured to start the flame of the torch by: instructing the CNC machine to move the torch away from the workpiece such that the first surface is not in contact with the second surface; directing the power source to charge an energy storage device associated with the torch; instructing the CNC machine to move the torch toward the workpiece; and directing the energy storage device to discharge while directing the torch to supply an ignition gas to a gap between the first surface and the second surface.
 10. The oxy-fuel thermal process system of claim 1, wherein the microprocessor is further configured to detect whether a flame is started by determining whether there is an electric response to a test current driven by the driver.
 11. The oxy-fuel thermal process system of claim 1, wherein the first surface and the second surface have the same geometry and comprise the same material, and wherein the first surface and the second surface are positioned in the flame in a symmetric relationship with respect to the torch.
 12. The oxy-fuel thermal process system of claim 1, wherein the microprocessor is further configured to calculate a temperature of the workpiece based on the information about the driven power source and the sensed electric response, to determine if the temperature reaches a predetermined level, and in response to determining that the temperature reaches the predetermined level, to initiate a cutting process for the workpiece.
 13. The oxy-fuel thermal processing system of claim 12, wherein, after the cutting process is initiated, the microprocessor is further configured to calculate a second temperature of the workpiece based on information about a second driven power source and a second sensed electric response, to determine if the second temperature falls below the predetermined level, and in response to determining that the second temperature falls below the predetermined level, to stop the cutting process for the workpiece.
 14. The oxy-fuel thermal processing system of claim 13, wherein, after the cutting process for the workpiece is stopped, the microprocessor is further configured to wait until a predetermined time is elapsed and then calculate a third temperature of the workpiece based on information about a third driven power source and a third sensed electric response, to determine if the third temperature reaches the predetermined level, and in response to determining that the temperature reaches the predetermined level, to resume the cutting process for the workpiece.
 15. The oxy-fuel thermal processing system of claim 2, wherein the first parameter is representative of imminent cut loss.
 16. The oxy-fuel thermal processing system of claim 2, wherein the first parameter is representative of a cut quality.
 17. The oxy-fuel thermal processing system of claim 1, wherein the microprocessor is further configured to calculate an extrapolation based on information about a plurality of driven power sources and sensed electric responses to determine a zero distance between the first surface and the second surface. 